The present invention relates to interconnect devices for providing electrical connections to printed circuit boards, and more particularly, to a molded connector having a plated living hinge which is formed integrally with a circuit board.
Efforts to reduce costs associated with electrical systems and packaging include those directed towards integrating components so that part counts and costs are reduced while increasing reliability. In particular, interests exist in the area of integrating connectors into printed circuit boards so that both are produced during the same plating and etching process. One such connector utilizes flexible printed circuits ("flex circuits") or "flex-film" circuits which are comprised of polyimide or polyester film having conductors printed upon a surface thereof. The flex circuit is then connected to a rigid circuit board by solder or by laminating the flex circuit upon the rigid circuit board. The flex circuit forms the conductive circuitry of the rigid circuit board and extends off the rigid circuit board to provide a flexible electrical connection to another object. The connector takes the form of a socket wherein flex circuit is laminated upon a circuit board having a rectangular aperture for accepting a male connector. The flex circuit has exposed conductors and extends into an area of the aperture. When the male connector is inserted, the flex circuit deflects into the aperture and contacts on the male connector make contact with the exposed conductors on the flex circuit. While flex circuits provide effective flexible electrical connections, their use necessitates the lamination of the flex circuit upon the rigid circuit board. The cost of production, both in terms of labor costs and the costs of providing and maintaining an increased number of parts, is increased over that of a normal printed circuit board.
Another method of providing a connector in a molded circuit board employs three dimensional plated circuits as disclosed in U.S. Pat. No. 4,985,116, "Three Dimensional Plating Or Etching Process And Masks Therefor", issued to Mettler et al. A rectangular recess is provided in a molded circuit board. Conductors are then plated on inside surfaces of the recess. A plug, inserted into the recess, has resilient contacts which make electrical contact with the conductors. This type of molded connector is useful in applications requiring the three dimensional plating. However, many applications do not require three dimensional plating. Three dimensional plating is more expensive than standard two dimensional plating and etching techniques used on flat circuit boards. Therefore, the use of such a connector is not necessarily advantageous where other plated three dimensional features are not required and two dimensional plating is otherwise sufficient.
Printed wiring boards are often used as backplanes for display and control panels. Specific applications, for example, include consumer electronics and automobile dashboards. The use of printed circuit boards as a backplane allows for the elimination of wire harnesses interconnecting manual controls and annunciators. Such circuit boards are molded in required configurations and incorporate either the flex circuit connector, the three dimensional connector, or a connector shell and pins affixed after molding or during molding. While use of the rigid printed boards as dashboard backplanes provides for significant cost savings in both assembly and parts count, competition dictates that further cost savings be continuously sought. Therefore, a requirement exists for an interconnection means which does not require flex circuit, three dimensional etching, or the incorporation of a separate connector shell, and which is less expensive than present methods.
Flex circuits permit bendable contacts to be formed and used in integral connectors. Typically, flex circuits are fabricated upon flexible polyester and polyimide films to which components may be soldered. A copper foil coated with an adhesive is laminated upon the flexible films. The required conductor patterns are then etched in the copper foil. Although flex circuit circuitry provides a practical solution in applications requiring a flexible circuit, a flex circuit cannot by itself provide rigidity in applications requiring positive support for components connected to the flex circuitry. Furthermore, while the polyester and polyimide materials are well suited for the formation of flexible films, neither can be used for injection molding. Therefore, where rigidity is required in a circuit board having molded features, such as a instrument cluster backplane, the flex circuit must be connected to or laminated upon a rigid substrate composed of a moldable material such as polypropylene.
Other substrate materials are also used with flex circuits. Such materials include polyetherimide, also known as "ULTEM" produced by the General Electric Corporation, polysulfone, ABS, and polycarbonate. These materials are typically used in circuit boards but are unsuitable for applications requiring flexibility because the material fracture if flexed.
There also exists a flexible circuit board material produced under the name "BEND FLEX" by the Roger's Corporation. This material is a copper laminate material which possesses a constant flexural modulus throughout. The material requires a relatively large bending radius compared to flex circuitry and does not possess sufficient rigidity for the mechanical support of fixed components required in most applications involving control and display backplanes.
Flexible plastic hinges, known in the trade as "living hinges", have been used in articles of manufacture requiring a hinged member where production of the entire article in a single molding step is desired. Plastics suitable for the formation of living hinges must endure stretching ratios as high as 2 or 3 to 1. Therefore, such plastics must possess the capability of high elongation beyond their yield point and a low modulus of elasticity. Acceptable plastics include polypropylene, polyethylene, and nylon. However, such characteristics, combined with low dimensional stability at elevated temperatures, are unacceptable for materials used in the production of circuit boards wherein rigidity and high-temperature stability are required.